全文获取类型
收费全文 | 40358篇 |
免费 | 3240篇 |
国内免费 | 2569篇 |
专业分类
化学 | 27809篇 |
晶体学 | 459篇 |
力学 | 1737篇 |
综合类 | 236篇 |
数学 | 4280篇 |
物理学 | 11646篇 |
出版年
2023年 | 300篇 |
2022年 | 383篇 |
2021年 | 840篇 |
2020年 | 858篇 |
2019年 | 929篇 |
2018年 | 773篇 |
2017年 | 756篇 |
2016年 | 1333篇 |
2015年 | 1298篇 |
2014年 | 1660篇 |
2013年 | 2534篇 |
2012年 | 3059篇 |
2011年 | 3390篇 |
2010年 | 2297篇 |
2009年 | 2199篇 |
2008年 | 2850篇 |
2007年 | 2661篇 |
2006年 | 2529篇 |
2005年 | 2292篇 |
2004年 | 1959篇 |
2003年 | 1544篇 |
2002年 | 1657篇 |
2001年 | 1170篇 |
2000年 | 982篇 |
1999年 | 624篇 |
1998年 | 444篇 |
1997年 | 426篇 |
1996年 | 454篇 |
1995年 | 342篇 |
1994年 | 347篇 |
1993年 | 336篇 |
1992年 | 319篇 |
1991年 | 250篇 |
1990年 | 183篇 |
1989年 | 173篇 |
1988年 | 174篇 |
1987年 | 138篇 |
1986年 | 108篇 |
1985年 | 185篇 |
1984年 | 118篇 |
1983年 | 102篇 |
1982年 | 123篇 |
1981年 | 90篇 |
1980年 | 87篇 |
1978年 | 93篇 |
1977年 | 88篇 |
1976年 | 97篇 |
1975年 | 102篇 |
1974年 | 81篇 |
1973年 | 104篇 |
排序方式: 共有10000条查询结果,搜索用时 248 毫秒
61.
62.
63.
GM(1,1)的周期修正模型及其在泉水流量预测中的应用 总被引:6,自引:2,他引:4
本文阐述了 GM( 1 ,1 )的残差周期修正模型 ,并将它应用于山西神头泉的流量预测中 ,建立了神头泉流量的 GM( 1 ,1 )周期修正模型 ,对其流量进行了预测 ,为神头泉域岩溶水资源开发利用和保护提供了科学依据 相似文献
64.
Sungyong Kim Lingxin Chen Sangyeop Lee Gi Hun Seong Jaebum Choo Eun Kyu Lee Chil-Hwan Oh Sanghoon Lee 《Analytical sciences》2007,23(4):401-405
A rapid DNA analysis has been developed based on a fluorescence intensity change of a molecular beacon in a PDMS microfluidic channel. Recently, we reported a new analytical method of DNA hybridization involving a PDMS microfluidic sensor using fluorescence energy transfer (FRET). However, there are some limitations in its application to real DNA samples because the target DNA must be labelled with a suitable fluorescent dye. To resolve this problem, we have developed a new DNA microfluidic sensor using a molecular beacon. By monitoring the change in the restored fluorescence intensity along the channel length, it is possible to rapidly detect any hybridization of the molecular beacon to the target DNA. In this case, the target DNA does not need to be labelled. Our experimental results demonstrate that this microfluidic sensor using a molecular beacon is a promising diagnostic tool for rapid DNA hybridization analysis. 相似文献
65.
Mid-infrared generation based on a periodically poled LiNbO3 optical parametric oscillator 下载免费PDF全文
We report a nanosecond Nd:YVO_4-pumped optical parametric oscillator (OPO) based on periodically poled LiNbO_3 (PPLN). Tuning is achieved in this experiment by varying the temperature and period of the PPLN. The design of double-pass singly resonant oscillator (DSRO) and confocal cavity enables the OPO threshold to be lowered considerably, resulting in a simple, compact, all-solid-state configuration with the mid-infrared idler powers of up to 466mW at 3.41μm. 相似文献
66.
67.
N. Wright und W. C. Lee 《Fresenius' Journal of Analytical Chemistry》1940,120(1-2):39-40
Ohne Zusammenfassung 相似文献
68.
CONG Fuzhong & LI YongSchool of Mathematics Information Science Shandong Institute of Business Technology Yantai China Office of Mathematics Changchun Flight Academy of the Air Force Changchun China Department of Mathematics Jilin University Changchun China 《中国科学A辑(英文版)》2004,47(5):675-686
An effective stability result for generalized Hamiltonian systems is obtained by applying the simultaneous approximation technique due to Lochak. Among these systems, dimensions of action variables and angle variables might be distinct. 相似文献
69.
70.
The transverse momentum spectra for pions observed by WA80 and NA35 collaborations are analysed within a fireball model with collective isentropic expansion and a realistic freeze-out criterion. By varing the initial state of the fireball, an excellent fit to the data is achieved for the whole measured range ofP T . Slight differences in the data for the spectral slopes from central and pheripheral collisions originate in our model from the difference in the size of the fireball and in the number of participating nucleons in central and peripheral collisions. Using additional information from two-pion correlations, we can extrapolate our model back from the freeze-out point (determined from the spectra) to the initial state; we find that an initial energy density of 1.5–2GGeV/fm3 is sufficient to explain the data from central O+Au collisions at 200A GeV. 相似文献